Subtopic Deep Dive
Conformational Analysis of Heterocycles
Research Guide
What is Conformational Analysis of Heterocycles?
Conformational analysis of heterocycles studies the preferred three-dimensional ring conformations and puckering modes of heterocyclic compounds using NMR, X-ray diffraction, and DFT calculations.
This subtopic examines ring inversion barriers, anomeric effects, and intramolecular interactions in five- and six-membered heterocycles. Key methods include low-temperature NMR for coupling constants (Lambert et al., 1967; Booth and Lemieux, 1971) and DFT for energy profiles (Björnsson and Árnason, 2009). Over 10 seminal papers span 1967-2020 with 1,500+ total citations.
Why It Matters
Conformational data from heterocycles guides design of bioactive molecules like quinoxaline antivirals (Montana et al., 2020, 130 citations) and NO donors from amidoximes (Sahyoun et al., 2019, 70 citations). Lambert and Featherman (1975, 155 citations) correlated pentamethylene heterocycle puckering with reactivity, enabling rational synthesis of constrained pharmaceuticals. Kleinpeter (2004, 80 citations) linked six-membered ring conformations to biological activity in drug scaffolds.
Key Research Challenges
Accurate DFT Energy Prediction
Standard functionals like B3LYP fail to capture dispersion in heterocycle conformations, overestimating chair-boat energies (Björnsson and Árnason, 2009). Silicon substitution effects require dispersion-corrected DFT for reliable barriers. Over 60 citations highlight persistent inaccuracies in relative energies.
Quantifying Anomeric Effects
Axial N-H preferences in oxazines challenge classical steric models, demanding low-temperature NMR (Booth and Lemieux, 1971, 79 citations). Coupling constant analysis reveals sole axial dominance in 1,3-diazanes. Experimental verification lags computational predictions.
Heterocycle π-Stacking Measurement
N-heterocycle stacking strengths vary with cationicity, complicating model systems (Li et al., 2013, 64 citations). Rigid equilibrium models quantify neutral vs. cationic pyridines. X-ray data integration remains inconsistent across scaffolds.
Essential Papers
Hydrogen bonding in sulfonamides
Daniel A. Adsmond, David Grant · 2001 · Journal of Pharmaceutical Sciences · 184 citations
Conformational analysis of pentamethylene heterocycles
Joseph B. Lambert, Sidney I. Featherman · 1975 · Chemical Reviews · 155 citations
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTConformational analysis of pentamethylene heterocyclesJoseph B. Lambert and Sidney I. FeathermanCite this: Chem. Rev. 1975, 75, 5, 611–626Publication Dat...
Quinoxaline Derivatives as Antiviral Agents: A Systematic Review
Marc Montana, Vincent Montero, Omar Khoumeri et al. · 2020 · Molecules · 130 citations
Background: In recent decades, several viruses have jumped from animals to humans, triggering sizable outbreaks. The current unprecedent outbreak SARS-COV-2 is prompting a search for new cost-effec...
Conformational Analysis of Saturated Heterocyclic Six-Membered Rings
Erich Kleinpeter · 2004 · Advances in heterocyclic chemistry · 80 citations
Conformational characterization of simple group VI heterocycles
Joseph B. Lambert, Robert G. Keske, Donnas K. Weary · 1967 · Journal of the American Chemical Society · 80 citations
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTConformational characterization of simple group VI heterocyclesJoseph B. Lambert, Robert G. Keske, and Donnas K. WearyCite this: J. Am. Chem. Soc. 1967, ...
The Anomeric Effect: The Conformational Equilibria of Tetrahydro-1,3-oxazines and 1-Methyl-1,3-diazane
H. Booth, René Lemieux · 1971 · Canadian Journal of Chemistry · 79 citations
By measurement of CH–NH coupling constants at low temperatures, the N–H axial conformation was shown to be the dominant, or sole, conformation for tetrahydro-1,3-oxazine, tetrahydro-2-methyl-1,3-ox...
Amidoximes and Oximes: Synthesis, Structure, and Their Key Role as NO Donors
Tanya Sahyoun, Axelle Arrault, Raphaël Schneider · 2019 · Molecules · 70 citations
Nitric oxide (NO) is naturally synthesized in the human body and presents many beneficial biological effects; in particular on the cardiovascular system. Recently; many researchers tried to develop...
Reading Guide
Foundational Papers
Start with Lambert et al. (1967, 80 citations) for group VI heterocycle NMR basics, then Lambert and Featherman (1975, 155 citations) for pentamethylene analysis, and Booth and Lemieux (1971, 79 citations) for anomeric effects establishing core principles.
Recent Advances
Study Björnsson and Árnason (2009, 62 citations) for DFT advancements, Montana et al. (2020, 130 citations) for antiviral applications, and Sahyoun et al. (2019, 70 citations) for NO-donor conformations.
Core Methods
NMR coupling constants at low temperatures (Lambert 1967); dispersion-corrected DFT for energies (Björnsson 2009); X-ray crystallography for stacking (Li 2013); equilibrium model systems for relative strengths.
How PapersFlow Helps You Research Conformational Analysis of Heterocycles
Discover & Search
Research Agent uses citationGraph on Lambert et al. (1975, 155 citations) to map pentamethylene heterocycle literature, then findSimilarPapers for 50+ related works on ring puckering. exaSearch queries 'DFT dispersion corrections heterocycle conformations' to surface Björnsson and Árnason (2009). searchPapers with 'anomeric effect oxazines NMR' retrieves Booth and Lemieux (1971).
Analyze & Verify
Analysis Agent applies readPaperContent to extract DFT energy tables from Björnsson and Árnason (2009), then runPythonAnalysis with NumPy to recompute B3LYP vs. dispersion-corrected barriers. verifyResponse (CoVe) cross-checks claims against Kleinpeter (2004) excerpts, achieving GRADE A evidence grading for conformational equilibria. Statistical verification confirms NMR coupling trends from Lambert et al. (1967).
Synthesize & Write
Synthesis Agent detects gaps in quinoxaline conformational data vs. antiviral activity (Montana et al., 2020), flagging contradictions in π-stacking (Li et al., 2013). Writing Agent uses latexEditText for ring puckering diagrams, latexSyncCitations to integrate 10 papers, and latexCompile for publication-ready reviews. exportMermaid generates conformational energy flowcharts.
Use Cases
"Plot DFT conformational energies for sila-heterocycles from Björnsson 2009 using Python."
Research Agent → searchPapers 'Björnsson Árnason 2009' → Analysis Agent → readPaperContent → runPythonAnalysis (pandas/matplotlib barrier plots) → matplotlib energy diagram output.
"Write LaTeX review of anomeric effects in 1,3-oxazines citing Booth Lemieux."
Synthesis Agent → gap detection on anomeric literature → Writing Agent → latexEditText (add oxazine structures) → latexSyncCitations (Booth 1971, Lambert 1967) → latexCompile → PDF review output.
"Find GitHub code for heterocycle conformational sampling from recent papers."
Research Agent → searchPapers 'heterocycle DFT conformational analysis code' → Code Discovery → paperExtractUrls → paperFindGithubRepo → githubRepoInspect → Python sampling scripts output.
Automated Workflows
Deep Research workflow conducts systematic review of 50+ heterocycle papers: searchPapers → citationGraph (Lambert 1975 hub) → DeepScan 7-steps with CoVe checkpoints on DFT claims. Theorizer generates hypotheses linking conformations to bioactivity from Montana (2020) and Sahyoun (2019), outputting energy-activity models. DeepScan verifies π-stacking data across Li (2013) and Kleinpeter (2004).
Frequently Asked Questions
What defines conformational analysis of heterocycles?
It determines 3D ring shapes, puckering, and inversion barriers in heterocycles via NMR, X-ray, and DFT, correlating to reactivity (Lambert and Featherman, 1975).
What are main methods used?
Low-temperature NMR measures coupling constants for axial preferences (Booth and Lemieux, 1971); DFT with dispersion corrections computes energies (Björnsson and Árnason, 2009); X-ray confirms solid-state puckering.
What are key papers?
Lambert and Featherman (1975, 155 citations) on pentamethylene rings; Kleinpeter (2004, 80 citations) on six-membered rings; Booth and Lemieux (1971, 79 citations) on anomeric effects.
What open problems exist?
Accurate dispersion modeling for heteroatom effects (Björnsson and Árnason, 2009); scaling conformational predictions to complex pharmaceuticals; integrating π-stacking with bioactivity (Li et al., 2013).
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